Computing devices (e.g., tablet computers, personal digital assistants) often include touch screens that enable the computing devices to detect touch commands and/or hover commands. For instance, a touch screen may include any of a variety of elements that are responsive to resistance, capacitance, and/or light for enabling detection of such commands. A touch screen usually includes a sensor matrix, which includes an array of row sensors and an array of column sensors. Each of the sensors in the arrays is typically configured to detect an object when the object is placed within a certain proximity to the sensor. For instance, an amount of resistance, capacitance, and/or light detected by the sensor may indicate whether the object is proximate the sensor. A location of the object with respect to the touch screen may be determined based on the amount(s) of resistance, capacitance, and/or light that are detected by one or more of the sensors.
A stylus is an object that is commonly used to provide input to a touch screen. For instance, the stylus may be used to write a message on the touch screen and/or to select icons that are displayed on the touch screen. It is desirable for a detected location of the stylus to be as close as possible to the physical location at which the stylus is touching the touch screen or being used to point at the touch screen. However, in practice, the detected location differs from the physical location, and the difference (referred to as the position error) typically increases as the stylus is tilted away from an orientation that is normal (i.e., perpendicular) to the touch screen.
An electrostatic stylus is a stylus that generates an active signal (e.g., broadcast signal) for detection by a capacitive sensor matrix. An active electrostatic stylus often is detectable at greater distances from a sensor matrix than a passive stylus. However, the configuration of a conventional active electrostatic stylus typically does not facilitate estimation of the tilt of the electrostatic stylus. For instance, the active signal induced by a conventional electrostatic stylus onto sensor matrix electrodes may be too localized in space (or equivalently, too weak at matrix electrodes which are not immediate neighbors of the contact point) to enable tilt angle estimation. Accordingly, electrostatic styluses traditionally are quite susceptible to position error.